In recent years, there has been a rapid expansion in the range of data communications and entertainment services available to consumers. For example, in addition to traditional television services, consumers can now receive a wide variety of video and audio services via cable and other terrestrial transmission media and also via direct satellite broadcast. There has also been a rapid expansion in the types of telephone and Internet services that can be delivered via cable or digital subscriber line transmission media.
A “set top box” (often placed on top of a TV set) provides customers with a centralized control center for integration and control of data and entertainment services. Set top boxes require signal processing circuits that are capable of processing radio-frequency (RF) signals, baseband signals, and digital signals. Typically, the components used in the set top box to perform RF signal processing and baseband processing were either formed from discrete components or formed in a bipolar or bipolar-Complementary Metal Oxide Semiconductor process (bipolar/CMOS process). Components of these types worked well in meeting the high demands of the set top box. However, these components were expensive to produce and typically required that the set top box include a large number of circuit components.
In order to address these shortcomings, it is desirable to fully service the requirements of the set top box with a very small number of integrated circuits (one integrated circuit in a fully minimized installation) that are formed in a CMOS process. Integrated circuits formed in CMOS processes are inexpensive, consume very little power, and generate very little heat. However, integrated circuits formed in CMOS processes often have higher rates of component mismatches, increased temperature-related variations, and other process variations. Therefore, factors such as noise, data transmission errors and non-linearity are generally more common in integrated circuits manufactured using CMOS processes.
One particular problem relating to the use of CMOS integrated circuits in set top boxes relates to the unit identification. Set top boxes are typically programmed with a unique identity. This unique identity is used by a corresponding service provider to enable the functionality of the set top box when deployed, to identify data retrieved from the set top box for billing purposes, and for other operational purposes relating to the set top box. This unique identity (and other information that is programmed a single time into the set top box) is stored in a One-Time-Programmable-Read-Only-Memory (hereafter referred to as OTP memory). Other devices such as cell phones, network cards, and other electronic devices also require identification that is stored in this manner.
When the components of the set top box are formed in CMOS processes, the OTP memory is also formed in the CMOS process. However, as is generally known, memory of the write-once/read-many type formed in CMOS processes is oftentimes not fully reliable. Such memory may include bad cells when constructed. If data is written to these bad cells, data read from these bad cells is also bad. Further, write-once/read-many memories formed in CMOS processes typically degrade over time such that, even though the cells are generally good when constructed, memory will be lost over time. The robustness of this type of memory formed in a CMOS process varies with the process and, unfortunately, is oftentimes not known until integrated circuits are formed and a particular percentage of the integrated circuits have failed due to failure of an OTP memory contained therein.
Unfortunately, when OTP memory becomes even partially non-functional, the operation of a corresponding device, e.g., set top box, is adversely affected. These same problems occur when an OTP memory is used to identify other types of devices, e.g., cell phones, network cards, personal computers, etc. Thus, there is a need for an OTP memory that overcomes problems relating to bad memory cells.